Tower of Hanoi Solver

// Imports
import java.util.Map;
import java.util.Stack;
import java.util.HashMap;

// Class
public class Solver {
    private int NumberOfDisks = 0;

    private Map<String, Stack<Integer>> Rods = new HashMap<>() {
        {
            put("A", new Stack<>());
            put("B", new Stack<>());
            put("C", new Stack<>());
        }
    };

    public Solver(int disks) {
        if (disks < 3) {
            throw new IllegalArgumentException("You need to have at least three disks.");
        } else {
            NumberOfDisks = disks;
            setup();
        }
    }

    public void solve() {
        reset();

        if (NumberOfDisks % 2 == 0) {
            solveTowerOfHanoi(0, "A", "C", "B");
        } else {
            solveTowerOfHanoi(0, "A", "B", "C");
        }

        System.out.println(Rods.get("A") + " " + Rods.get("B") + " " + Rods.get("C"));
    }

    private void solveTowerOfHanoi(int state, String from, String intermediary, String to) {
        if (!Rods.get("A").empty() || !Rods.get("B").empty()) {
            moveDisk(from, to);

            if (state == 0) {
                solveTowerOfHanoi(1, from, to, intermediary);
            } else {
                solveTowerOfHanoi(0, intermediary, from, to);
            }
        }
    }

    private void moveDisk(String rodKey1, String rodKey2) {
        Stack<Integer> rod1 = Rods.get(rodKey1);
        Stack<Integer> rod2 = Rods.get(rodKey2);

        Integer ring1 = !rod1.empty() ? rod1.peek() : NumberOfDisks;
        Integer ring2 = !rod2.empty() ? rod2.peek() : NumberOfDisks;

        if (ring1 < ring2) {
            rod2.push(rod1.pop());
        } else {
            rod1.push(rod2.pop());
        }
    }

    private void setup() {
        for (int index = NumberOfDisks - 1; index >= 0; index--) {
            Rods.get("A").push(index);
        }
    }

    private void reset() {
        for (Stack<Integer> rod : Rods.values()) {
            while (!rod.empty()) {
                rod.pop();
            }
        }

        setup();
    }
}